Method for truing gears and the like



Jan. 8, 1929. I 1,698,215

A. w. COPLAND ET AL METHOD FOR TRUI'NG GEARS AND THE LIKE Filed March 25, 1927 [v mmmmm E {Ada /V7025:

Ame/v54 Patented Jan. 8, 1929. v

UNITED STATES PATENT OFFICE.

ALEXANDER w. ooTLA D, OE'DIR IINGIIAM, MICHIGAN, AND MAXWELL I. MATHEW- SON, OF PROVIDENCE, RHODE ISLAND, AssIGNoRs To DETROIT AND sEOoRITY TRUsT comrANY, or DETROIT, MICHIGAN, A CORPORATION E MICHIGAN.

METHOD EOR TR'DING GEARS AND THE LIKE.

Application filed March 28, 1927, Serial No. 177,743, and in Great Britain September 14,1926.

The invention relates to the art of truing gears by grinding or la ping, and more particularly to an improve form of lap suitable for use in the la ping of gearsby applicants '5' method as set firth-in their copending'application Serial No. 551,141, filed- April 10.-

1922. The present application is in part a continuation of'a divisible .part of our pending application Serial No. 551,140, filed April 10, 1922. It may also be considered a similar continuation in part of our application Serial No. 551,141 referred to above; its

purpose being toshow a relation between features of both, which, though obvious when 5 both are considered together, was not as fully indicated in either as applicants desire.

The method of our application SerialNo.

551,141 is applicable to the truing of various bodies which have radiating surfaces uniformly spaced in circular series, butthe method is especially useful in the lapping of gears and for the sake of simplicity, We willinter-meshing gears, then one is reciprocated with respect to the other in mutual abrasive contact, and intermittently one is progressively rotatably advanced in relation to the other to change the registration of the teeth. If the gear is a spur gear, the lap of course takes the'form of an internal gear and, vice versa, if the gear to be'lapped is an internal 0 ear, the lap takes 'th'e" form. of a spur gear. The lap is preferably elongated or widened axially in order to afiord adequate abrasive area.

In such a lapping or grinding operation the amount of grinding or abrading of a surface sliding in contact with another surface is dependent first, on the character of the abrasive material used; second on the area of abrading surface that is moved Over each unit area 5 of the surface to be ground or trued; and third, the amount of pressure perunit area of contact. I

The invention has for its chief object the provision of an improved method of the general character disclosed in our application Serial No. 551,141, by the use of which it is possible to vary the second of the three factors above noted and thereby control the amounts of material ground ofi from different portions of'the teeth of the gear tobe lapped. I In the accompanying drawing we show a.

paratus suitable for the carrying out of t e invention. In the drawings,

4 Fig. 1 is a longitudinal section through an annular, internally toothed lap.

FFlg. 2 is a cross section on the line 22"of 1g. Fig. 3 is a view corresponding to Fig. 1

showing a modified form of construction.

Fig. 4 is a diagrammatic view illustrating Referring first to the diagram of Fig.4,

the operation of the a paratus-disclosed in the gear wheel A, or other object to be ground,

is fixed to the arbor B which is rotatably supported on the centering spindle C having a fixed connectionwith the frame of the machine. A lap D, having corresponding projections adapted to register with the gear teeth, is mounted to reciprocate vertically rel ativeto the gear to be ground. This vertical reciprocation is effected bymeans of the arm E which is connected atone end to the lap and is operated as shown by means of a suitable crank F and link F. We have shown by full, dotted, -and dot and dash lines three positions of the lap D and its operating mechanlsm during their travel;

Inorder to insure a grinding contact between the mutuall engaging surfaces a torsional force is app ied to the gear wheel during its engagement with the lap. The ratchet wheel G is fixed to a rotatably mounted member H which carries projections I fitting in slotsformed in the member L tion R for engaging the rod P to actuate the same to place a tension on the spring 0. The

.parts are so constructed and arranged that when the gear wheel is out of engagement with the lap (which occurs at each end of its stroke) no ressure will be exerted by the cam on the rod and consequently the spring O will be at zero tension. The arrangement of parts is such that as the teeth of the lap enter into, and leave, engagement with the teeth of the gear to be ground, the inclined surfaces of the cam portion will move into, and out of, engagement with the rod P, a d as a result the torsional pressure between t' e contacting surfaces of the gear and lap teeth will be progressively increased and decreased as they are brought into and out of engagement, respectively. It will thus be seen that during the period that the cam portion R is in operative engagement with the rod P a torsional force is being applied to the gear wheel which will result in the setting up of a grinding contact between the mutually enga ing surfaces.

As stated, in the operation 0 the apparatus as above indicated, the gear and lap move out of mutual engagement at the end of each stroke of the lap, and in carrying out the method of our application Serial No. 551,141, during such disengagement of the gear and lap we efiect (by means not shown in the dia gram) redetermined relative angular move? ment 0? the gear and lap, to intermittently challilge the registration of the gear and'l'ap teet The chief results attained by the method just described are the accurate equi-spacing of the teeth of the gear, and the averaging of the tooth contours of the gear. In case the tooth contours of the gear to be trued approximate the true involute or other form desired, the method which has been described will give satisfactory results. On the other hand if the initial tooth contours vary substantially from the form desired, as by having too great fullness at the. crown, or too reat fullness near the root of the tooth, then the true predetermined contour desired cannot be attained by the said method. Again, in case it should be desired to effect a definite predetermined change in the tooth contour of a gear,.as by removing more of the metal or less of the metal from the piown portion than from the root portion of e tooth, this cannot be accomplished by the above described method. In carrying out our present invention, however, we provide an improved form of lap which is app 'cable to the method above described and by use of which the ends las referred to above can be attained.

Referring first to the form of lap shown in Figs. 1 and 2, it will be noted that thelap D is, generally speaking, in the form of an axially elongated internal ear having its cylindrical bod 1 formed with internal teeth-2. These teeth 2 are interrupted circumferentially by series of grooves 2, 2, which grooves are relatively narrow at the roots of the teeth 2 and widen toward the inner ends or crowns of the teeth.

- When a spur gear is lapped in register with a lap of. this character and by the method above described, it will be seen that the grinding effect on the sides of the gear teeth is progressively less from the roots of said teeth toward the crowns thereof than if the teeth of the lap were not grooved or cut away. The lap of this special form thus makes it possible to (1) true the teeth of gears which are too thick near theircrowns or (2) reduce the thickness of the ear teeth near their crowns to a value less t an the normal or true thickness.

'By varying the form of the interruptions or grooves cut in the teeth of the lap various modifications of the lapping action may be secured. For example in Fig. 3 is shown a lap D having its longitudinal internal teeth 4: interrupted by a series of circumferential grooves 4 which are wider near the roots of the lap teeth and gradually grow narrow towards the crowns of said teeth. Obviously the effect of grooves of this character is to lessen the grinding action of the lap upon the sides of the gear teeth near their crowns.

Various other modifications of lap teeth may be used and by predetermining the form of the lap any desired correction in the tooth form of the gear can be obtained. Thus, with our improved form of lap gear teeth of given contour can be modified to a predetermined' contour as well as being corrected in spacing, with a minimum amount of lapping. In considering the action of the modified lap, it is to be borne in mind that the abrasive action is mutual, effecting the lap as well as the.

ear.

It will be understood that the forms of apparatus and the procedure herein set forth can be varied widely without departing from the invention as defined the appended scoping relation and causing relative axial travel between the lap and body while exerting a pressure in an an lar direction to maintain abrasive contact etween the radial faces of the body and lap.

2. An improvement in the art of truing toothed bodies such as gears, which consists in providin a toothed lapcomplementary to the body to etrued with its teeth spaced on a means pitch circle substantially equal in diameter to the pitch circle of the body to be trued, the radial faces of which lap are partially cut away to an extent varying with the radial distance from the axis of the lap; assembling such toothed body and lap in concentric telescoping relation and causing relative axial reciprocation between the lap and body while exerting a pressure in an angular direction 10 to maintain abrasive contact between the radial faces of the body and lap; and during said reciprocation intermittently causing predetermined relative angular movement of the body and lap while they are out of mutual e'ngagement and thereby changing the registration of the body and lap teeth.

In testimony whereof, we hereunto afix our signatures.

ALEXANDER W. COPLAND. MAXWELL I. MATHEWSON. 

